Foil plating for semiconductor packaging

ABSTRACT

Arrangements for plating a single surface of a thin foil are described. In one aspect, a metal foil is wrapped tightly at least partially around a plating solution drum. The drum is partially immersed in a plating solution such that the waterline of the metal plating solution is below a break point where the metallic foil strip begins to unwind from the plating solution drum. With this arrangement, one side of the metallic foil strip is exposed to the metal plating solution, while the opposing back side of the metallic foil strip does not come in substantial contact with the metal plating solution. In this manner, the exposed side of the foil is plated while the back surface of the foil is not plated. The drum may be rotated to convey the foil through the plating solution.

FIELD OF THE INVENTION

The present invention relates generally to the packaging of integratedcircuits (ICs). More particularly, the invention relates to methods,apparatuses and systems for plating thin foils.

BACKGROUND OF THE INVENTION

There are a number of conventional processes for packaging integratedcircuit (IC) dice. By way of example, many IC packages utilize ametallic leadframe that has been stamped or etched from a metal sheet toprovide electrical interconnects to external devices. The die may beelectrically connected to the leadframe by means of bonding wires,solder bumps or other suitable electrical connections. Often, the dieand portions of the leadframe are encapsulated with a molding materialto protect the delicate electrical components on the active side of thedie while leaving selected portions of the leadframe exposed tofacilitate electrical connections to external devices.

At various times, package designs have been proposed that utilize ametal foil as the electrical interconnect structure in place of theleadframe. Although a number of foil based designs have been developed,none have achieved widespread acceptance in the industry in part becausefoil based packaging processes tend to be more expensive thanconventional leadframe packaging. Accordingly, there are continuingefforts to develop more efficient techniques that improve the costcompetitiveness of foil based packaging.

When a metal foil is used to form the interconnects of an integratedcircuit package, it is sometimes desirable to pre-plate one side (andonly one side) of the foil with a thin metal layer. For example, inpackages that utilize gold bonding wires to electrically connect a dieto a copper foil, it may be desirable to silver plate the side of thefoil that forms the wire bonding surface. This may be desirable because,as is well known in the art, gold does not adhere well to copper butdoes adhere reasonably well to silver plating. Thus, an intermediatesilver layer may be used to help anchor the bonding wires more securelyto the foil.

One way to silver plate selected portions of a foil would be to maskportions of the foil that are not to be plated with a dielectric whileleaving portions of the foil that are to be plated exposed. The exposedportions of the foil may then be plated using conventionalelectroplating techniques. Although such a masking approach works well,more cost effective methods for pre-coating a single side of a metalfoil are desirable. The present invention provides improved processesfor plating foils suitable for use in semiconductor packaging.

SUMMARY OF THE INVENTION

To achieve the foregoing and other objects of the invention improvedarrangements for plating just one side of an electrically conductivefoil are described. In one aspect, a metal foil is wrapped tightly atleast partially around a plating solution drum. The drum is partiallyimmersed in a plating solution such that the waterline of the metalplating solution is below a break point where the metallic foil stripbegins to unwind from the plating solution drum. With this arrangement,one side of the metallic foil strip is exposed to the metal platingsolution, while the opposing back side of the metallic foil strip doesnot come in substantial contact with the metal plating solution. In thismanner, the exposed side of the foil is plated while the back surface ofthe foil is not plated. The drum may be rotated to convey the foilthrough the plating solution.

In some embodiments, the metallic foil strip is drawn from an externalsource, such as a coil of metallic foil that is positioned away from theplating solution. In other embodiments, the metallic foil may be formedinto a coil that is partially submerged within the metal platingsolution. In such an arrangement, only one side of the outermost layerof the coil is exposed to the metal plating solution. The opposite sideof the metallic foil strip is pressed tightly against a turn in themetallic foil coil such that the metal plating solution does not come insubstantial contact with that surface.

Various drums, cleaning stations, drying stations and/or othercomponents can be incorporated into a plating system that includes theaforementioned apparatus. For example, some embodiments of the presentinvention involve one or more tensioner drums that are positioned alongthe path of the metallic foil strip to help maintain tension in themetallic foil strip. One or more cleaning stations can be arranged toclean sections of the metallic foil strip before and/or after plating.The metallic foil strip can be unwound from a foil coil before beingwound partially around the plating solution drum and passed through themetal plating solution. A receiving drum can be used to recoil sectionsof the metallic foil strip after plating. The plating solution drum caninclude a silicone or rubber surface that elastically receives themetallic foil strip and helps prevent the metal plating solution fromslipping underneath the strip. Still other embodiments relate to methodsfor operating the above apparatuses.

Another aspect of the present invention relates to an apparatus thatuses a fountain of metal plating solution to plate a metal on one sideof a metallic foil strip. In this aspect, a solution emitting device isfluidly coupled with a container of metal plating solution and faces aportion of a side of a metallic foil strip. Two electrodes are arrangedto conduct an electrical current through the fountain and the metallicfoil strip. The apparatus is arranged to move the metallic foil stripsuch that different portions of the metallic foil strip pass in front ofthe solution emitting device. The solution emitting device generates afountain of metal plating solution that comes in contact with one sideof the metallic foil strip. As more of the metallic foil strip passes infront of the solution emitting device and comes in contact with thefountain, more of one side of the metallic foil strip is plated withoutsubstantially plating metal on the other side of the metallic foilstrip.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and the advantages thereof, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a diagrammatic side view of a plating apparatus according toone embodiment of the present invention.

FIG. 2 is a diagrammatic side view of a system that uses the platingapparatus of FIG. 1 and various stations to clean, dry and electroplatea metal onto a metallic foil strip according to one embodiment of thepresent invention.

FIG. 3 is a diagrammatic side view of a plating apparatus that involvespartially submerging a foil coil in a metal plating solution accordingto another embodiment of the present invention.

FIG. 4 is a diagrammatic side view of a system that uses the platingapparatus of FIG. 3 and various stations to clean, dry and electroplatea metal onto a metallic foil strip according to one embodiment of thepresent invention.

FIG. 5 is a diagrammatic side view of a system that uses a fountain ofmetal plating solution to plate metal on a surface of a metallic foilstrip in accordance with one embodiment of the present invention.

FIG. 6A is a diagrammatic side view of another embodiment of the presentinvention that uses a fountain to plate metal on a surface of a metallicfoil strip.

FIG. 6B is an enlarged side view of the fountain and a portion of themetallic foil strip illustrated in FIG. 6A accordance with oneembodiment of the present invention.

In the drawings, like reference numerals are sometimes used to designatelike structural elements. It should also be appreciated that thedepictions in the figures are diagrammatic and not to scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present application describes a variety of improved processes forplating just one side of a foil. In the first described embodiment, ametallic foil strip is tightly wrapped around at least a portion of adrum. The drum is positioned within a container that contains a metalplating solution such that a portion of the metallic foil strip isimmersed in the metal plating solution. The exposed surface of themetallic foil is then electroplated, while the opposing, unexposedsurface of the metallic foil strip is pressed against the drum therebypreventing plating of the unexposed surface. The drum is rotated toconvey the metallic foil strip through the metal plating solution. Inthis manner, a single side of the metallic foil strip can be plated.

Referring now to FIG. 1, an exemplary plating apparatus 100 forelectroplating a metal onto a metallic foil strip will be described. Theplating apparatus 100 includes a metal plating solution 104 in acontainer 102, a metallic foil strip 108, a plating solution drum 110,and first and second electrodes 124 a and 124 b. Portions of the platingsolution drum 110 and the metallic foil 108 are submerged below thewaterline 118 of the metal plating solution 104. The metallic foil strip108 is wound partially around the plating solution drum 110. First andsecond electrodes 124 a and 124 b are electrically coupled with themetal plating solution 104 and the metallic foil strip 108,respectively.

The apparatus is designed to plate a metal, such as silver, onto justone surface of the metallic foil strip 108. To this end, first andsecond electrodes 124 a and 124 b are arranged to conduct an electricalcurrent through the metallic foil strip 108 and the metal platingsolution 104. The second surface 120 b is pressed tightly against theplating solution drum 110 so that the exposure of the second surface 120b to the metal plating solution 104 is limited. As a result, metal isplated on the first surface 120 a but not substantially on the secondsurface 120 b of the metallic foil strip 108.

In the illustrated embodiment, the metallic foil strip 108 and theplating solution drum 110 are partially immersed in the metal platingsolution 104 such that the waterline 118 is below the one or more breakpoints 112 where the metallic foil strip 108 begins to unwind from theplating solution drum 110. The plating solution drum 110 is submerged toa depth that is less than the radius 126 of a cross section of theplating solution drum 110. This arrangement helps ensure that onlyportions of the metallic foil strip 108 that are pressed against theplating solution drum 110 are immersed within the metal plating solution104.

The metallic foil strip 108 may be formed from any suitable electricallyconductive material and may be of any appropriate thickness, so long asthe foil is flexible enough to wrap tightly around the plating solutiondrum 110. By way of example, copper foil having a thickness in the rangeof about 8 and 35 microns are desirable for many applications, althoughit should be appreciated that thicker or thinner foils may be used aswell.

In some applications, it may be desirable to prevent metal from beingplated on the edges of the metallic foil strip 108. In such embodiments,the edges of the metallic foil strip 108 can be coated with a dielectricmaterial. In one implementation, the dielectric material is applied atthe ends of a cylinder formed by coiling the metallic foil strip 108.The metallic foil strip 108 may then be unwound from the coil and passedthrough apparatus 100. In such an arrangement, the dielectric materialthat covers the edges of the foil helps prevent plating of the edges.

The surface of the plating solution drum 110 may be formed from anymaterial, so long as it forms a good seal with the foil immersed in theplating solution. In some embodiments, the surface of the drum is formedfrom a dielectric material having elastic properties. The elasticsurface, which can be formed from silicone, rubber and/or other suitablematerials, helps form a tighter seal between the metallic foil strip 108and the plating solution drum 110.

In the illustrated embodiment first and second electrodes 124 a and 124b are arranged to provide an electrical potential difference between thefoil and the plating solution to provide the electrical currentnecessary to facilitate electroplating. The electrodes may be placed atany location that is suitable for conducting an electrical currentthrough the metal plating solution 104 and the metallic foil strip 108.By way of example, the first electrode 124 a may be directly connectedto the container 102 and/or suspended within the metal plating solution104. The second electrode 124 b may take the form of a metallic brushthat maintains an electrical connection with the metallic foil strip 108while the metallic foil strip 108 is in motion. Alternatively oradditionally, the second electrode 124 b can be directly connected tothe plating solution drum 110 or to a foil conveyor roller.

In the illustrated embodiment, the container 102 is open ended and themetallic foil strip 108 extends vertically downward into the container102, curves around the plating solution drum 110 and then extendsvertically upward out of the container 102. In other implementations,the container 102 can be closed or open and the metallic foil strip 108can extend through the container 102 and connect with the platingsolution drum 110 at a variety of other angles/directions, so long asthe break points where the foil first touch and first separate from theplating solution are sufficiently clear of the plating solutionwaterline to prevent the plating solution from contacting the backsurface of the foil.

Referring next to FIG. 2, another embodiment of the present inventionwill be described. In this embodiment, the plating apparatus 100 of FIG.1 is combined with various additional components to form a system forprocessing and plating metal on one side of a metallic foil strip 108.System 200 includes a foil coil 202, first and second sets of cleaningstations 208 a and 208 b, first and second tensioner drums 204 a and 204b, drying station 210 and a receiving drum 206. The system 200 isarranged to unwind a section of the metallic foil strip from a coil,pass the section through various cleaning, plating and drying modules,and then rewind the section.

In the illustrated embodiment, foil coil 202 serves as the initialsource of the metallic foil strip 108. It should be noted that althougha coil is a convenient way to store portions of a long metallic foilstrip 108, the metallic foil strip 108 can be in various forms (e.g., indifferent compact configurations, fed in from another processingoperation, etc.) prior to being passed through the system 200. A sectionof the metallic foil strip 108 is then passed through a first set of oneor more cleaning stations 208 a. The cleaning stations 208 a help removeundesirable residues and/or contaminants from the section of themetallic foil strip 108 by spraying water, solvents, detergents, acidsand/or other cleaning solutions on the first and/or second surfaces 120a and 120 b of the section as appropriate. The cleaning of the sectionmay be performed in various ways e.g., spraying, immersing the metallicfoil strip 108 in a cleaning solution, etc.

Afterward, the section of the metallic foil strip 108 is passed around afirst tensioner drum 204 a. The first tensioner drum 204 a is arrangedto help reduce slack in the metallic foil strip 108. The increasedtension helps press the metallic foil strip 108 more tightly against theplating solution drum 110, which in turn helps prevent the substantialplating of a metal on the second (back) surface 120 b of the metallicfoil strip, as discussed earlier in connection with FIG. 1.

The section of the metallic foil strip 108 then moves around the platingsolution drum 110 and through the metal plating solution 104. A currentis conducted through the metallic foil strip 108 and the metal platingsolution 104, which results in the electroplating of metal on the firstsurface 120 a of the section of the metallic foil strip 108. Asdiscussed in connection with FIG. 1, substantially no metal is platedonto the second surface 120 b of the metallic foil strip 108.

After the section is plated, it travels partially around the secondtensioner drum 204 b, which, similar to tensioner drum 204 a, isarranged to help maintain tension in the metallic foil strip 108. Theplated section of the metallic foil strip 108 then passes through asecond set 208 b of one or more cleaning stations. Similar to thecleaning stations 208 a, the cleaning stations 208 b apply one or morecleaning fluids to one or both sides of the section. The plated andcleaned section is then passed by a drying station 210, which utilizesheat, air and/or other means to dry the section of the metallic foilstrip 108. Finally, the section is rewound or otherwise collected by thereceiving drum 206. The aforementioned process may be performed as acontinuous process with a moving conveyor of metal foil, or it may berepeated in sections by moving the metallic foil strip 108 in discreetsteps. Either way, the foil may be drawn from the coil 202 andultimately rewound at the receiving drum 206.

The speed with which the metallic foil strip is passed through the metalplating solution 104 and the magnitude of the electrical current that isconducted through the metallic foil strip 108 and the metal platingsolution 104 influences the thickness of the metal that is plated ontothe first surface 120 a of the metallic foil strip 108. In variousembodiments, system 200 is coupled with a computing device that enablesthe setting of the speed, current, metal thickness and/or otherparameters.

In the illustrated embodiment, the metallic foil strip 108 is inconstant motion. This motion can be maintained in various ways,including rotating the metallic foil strip 108 using one or more drums,pulling a portion of the metallic foil strip 108, etc. In someimplementations, a section of the metallic foil strip 108 does not stopmoving from the time that it is unwound from the coil 202 to the timethat it is rewound at receiving drum 206. In other embodiments, themetallic foil strip 108 stops moving periodically so that the cleaning,plating and/or drying operations can be applied to a particular portionof the metallic foil strip 108 for a sustained period of time.

Still another embodiment of the present invention is illustrated in FIG.3. Plating apparatus 300 includes a metal plating solution 304 in acontainer 302, a metallic foil strip 308, a plating solution drum 310,and first and second electrodes 324 a and 324 b. In this embodiment, acoil 309 of metallic foil strip 308 is wrapped around a metal platingdrum 310. The coil 309 is partially submerged in the metal platingsolution 304. Thus, in this embodiment, the coil 309 is positioned inthe metal plating solution 304 and is unwound within the container 302.

Plating apparatus 300 is arranged to perform a plating process thatplates metal primarily on the first surface 320 a and not on the secondsurface 320 b of the metallic foil strip 308. To this end, the metallicfoil strip 308 is tightly coiled around the plating solution drum 310.As a result, while the first surface 320 a of an outermost section 311of the metallic foil strip 308 is exposed to the metal plating solution304, the back surface 320 b of the section 311 is pressed tightlyagainst a turn 313 of the coil 309, thus helping to prevent the metalplating solution 304 from coming in substantial contact with the backsurface 320 b. When first and second electrodes 324 a and 324 b are usedto conduct an electrical current through the metal plating solution 304and the metallic foil strip 308, metal is plated on the first surface320 a of the metallic foil strip 308 and not substantially plated on thesecond surface 320 b.

To help limit the plating of metal to just the first surface 320 a, thewaterline 318 of the metal plating solution 304 is positioned below abreak point 312 where the metallic foil strip 308 begins to unwind fromthe coil 309 and where the second surface 320 b of the metallic foilstrip 308 starts to peel away from the coil 309 and become exposed. Thecoil 309 is submerged to a depth that is less than the radius 326 of thecoil.

Almost any of the features described in connection with FIGS. 1-2 can beused to modify corresponding features of the plating apparatus 300. Forexample, the unwinding of the coil 309 and the moving of the metallicfoil strip 308 can be performed by rotating the plating solution drum310, pulling a leading edge and/or a portion of the metallic foil strip308, etc. As described above, a dielectric coating can be applied to theedges of the metallic foil strip 308 and/or coil 309 to help limit theplating of metal to the first surface 320 a. The speed of the unwindingof the coil and/or the magnitude of the current between the first andsecond electrodes 324 a and 324 b can be adjusted to help control thethickness of the metal that is electroplated on the first surface 320 aof the metallic foil strip 308. The first and second electrodes 324 aand 324 b can be arranged in almost any manner suitable for maintainingan electrical current through the metallic foil strip 308 and the metalplating solution 304.

FIG. 4 illustrates an additional embodiment where the plating apparatus300 of FIG. 3 is integrated into a system 400 that cleans, dries, andrecoils the metallic foil strip 308. System 400 includes the platingapparatus 300, the metallic foil strip 308, a tensioner drum 404, a setof cleaning stations 408, a drying station 410 and a receiving drum 406.Metallic foil strip 308 extends from the foil coil 309, extendspartially around the tensioner drum 404, past the cleaning stations 408and the drying station 410 and then is ultimately recoiled by thereceiving drum 406.

The tensioner drum 404 helps increase tension in the metallic foil strip308, which in turn helps press an outer section 311 of the foil coil 309more firmly against an inner turn of the foil coil 309, as discussedearlier in connection with FIG. 3. This helps substantially limit theplating of metal to the first surface 320 a of the metallic foil strip308.

Plated sections of the metallic foil strip 308 then move past thecleaning stations 408. Cleaning stations 408 are arranged to spraycleaning solution, water and/or other suitable cleaning solvents ontothe metallic foil strip 308. The cleaned, plated section of the metallicfoil strip 308 is then dried by drying station 410 and recoiled orotherwise arranged in a compact form by receiving drum 406. It should beappreciated that the drums, stations and other components of the system400 can be modified using any of the features described in connectionwith FIG. 2.

Referring to FIG. 5, another aspect of the present invention isdescribed. System 500 uses a fountain 505 of metal plating solution toplate a single surface of metallic foil strip 508. The system 500includes a metallic foil strip 508 drawn from a foil coil 506, first andsecond sets of cleaning stations 514 a and 514 b, first and secondelectrodes 510 a and 510 b, a metal plating solution (not shown) in acontainer 502, a fountain 505 of metal plating solution that is emittedby a solution emitting device 507, a drying station 516 and a receivingdrum 512. The metallic foil strip 508, which is drawn from the coil 506,passes through the system 500 and is ultimately recoiled at receivingdrum 512. The solution emitting device 507 is fluidly coupled with thecontainer 502 and can generate a fountain 505 from the metal platingsolution in the container 502. The fountain 505 is continually generatedby the solution emitting device 507 such that the fountain 505 is incontact with the metallic foil strip 508 for a sustained period of time.The first and second electrodes are arranged to conduct an electricalcurrent through the fountain 505 and the metallic foil strip 508. As aresult, as sections of the metallic foil strip 508 pass through thefountain, metal is plated on these sections.

The solution emitting device 507 is arranged to direct the fountain 505towards a first surface 503 a of the metallic foil strip 508. In theillustrated embodiment, the fountain 505 directly strikes one or moreimpact regions on the first surface 503 a. Surface tension helps themetal plating solution spread out beyond the impact regions and acrossthe first surface 503 a. As a result, portions of the first surface 503a are coated with the metal plating solution and plated with a metaleven when they have not been directly struck by the fountain 505. Themetal plating solution, however, tends not to come in substantialcontact with the opposing second surface 503 b of the metallic foilstrip 508.

It should be appreciated that the illustrated embodiment can be modifiedto address the needs of various applications. For example, although onlyone fountain 505 is depicted, there could also be more than onefountain. The fountain 505 can take various forms, including one or morestreams, geysers, jets, sprays, etc. In the illustrated embodiment, thefountain 505 is projected in a direction approximately perpendicular tothe first surface 503 a of the metallic foil strip 508. In otherimplementations, one or more fountains can each approach the metallicfoil strip 508 from almost any angle or direction. The first electrode510 a can be electrically coupled with and/or directly connected to thefountain 505, the metal plating solution and/or the container 502. Thesecond electrode 510 b can maintain an electrical connection with themetallic foil strip 508 using any of the features described inconnection with second electrode 124 b of FIG. 1.

The first and second sets of cleaning stations 514 a and 514 b cleansections of the metallic foil strip 508 before and after they are platedby the fountain 505, respectively. The cleaned and plated sections ofthe metallic foil strip 508 are then dried by drying station 516 beforebeing wound around receiving drum 512. The cleaning stations 514 a and514 b, the drying station 516 and other parts of system 500 can havefeatures similar to the corresponding components described in connectionwith FIGS. 2 and 4.

Referring to FIG. 6A, another embodiment of a foil plating system 600 isdescribed. System 600 includes a foil coil 506, a metallic foil strip508 having first and second surfaces 503 a and 503 b, a first set of oneor more cleaning stations 614 a, a second set of one or more cleaningstations 614 b, first and second sets of guard rollers 609 a and 609 b,plating fountain 605, a solution emitting device 607, a platingcontainer 611 having a metal plating solution (not shown), first andsecond electrodes 510 a and 510 b, a drying station 516 and a receivingdrum 512. Various components of the foil plating system 600, includingfoil coil 506, metallic foil strip 508, first and second electrodes 510a and 510 b and receiving drum 512, resemble those described inconnection with FIG. 5 and can perform in an analogous manner to plate asingle side of the metallic foil strip 508. Foil plating system 600 hasadditional features to help improve the efficiency and effectiveness ofthe plating process.

For example, a first set of one or more guard rollers 609 a are arrangedto prevent chemical contamination between the cleaning and/or metalplating solutions. First set of guard rollers 609 a is positioned alongthe path of the metallic foil strip 508 between the first cleaningstation 614 a and the plating fountain 605. After a section of themetallic foil strip 508 is cleaned by the cleaning station 614 a using acleaning solution, the cleaned section is passed through the first setof guard rollers 609 a. In the illustrated embodiment, the guard rollers609 a are pressed flush against opposing first and second surfaces 503 aand 503 b of the metallic foil strip 508. As the guard rollers 609 arotate to help pass through sections of the metallic foil strip,cleaning solution residue is wiped, squeezed, absorbed and/or otherwiseremoved from the first and second surfaces 503 a and 503 b of themetallic foil strip 508. As a result, when the cleaned section comes incontact with the fountain 605 of metal plating solution, the risk anddegree of chemical contamination of the metal plating solution by thecleaning solution is reduced. After sections of the metallic foil strip508 have been plated through contact with the fountain 605, they arethen moved through the second set of guard rollers 609 b. The second setof guard rollers 609 b, which are positioned along the path of themetallic foil strip 508 between the plating fountain 605 and the secondset of cleaning stations 614 b, is similarly arranged to remove metalplating solution from sections of the metallic foil strip 508. Thisfeature helps limit cross-contamination between the metal platingsolution and the cleaning solution later applied by the second set ofcleaning stations 614 b. It should be appreciated that the number and/orlocations of the guard rollers may vary widely, depending on the needsof a particular application. Generally, guard rollers can be positionedin almost any location of the plating system 600 where they can helpprevent undesirable chemical reactions between different solutions thatare applied at different times to the metallic foil strip 508.

Plating system 600 further includes a solution emitting device 607 and aplating container 611 that are arranged to collect and reuse metalplating solution. In a process similar to the one described inconnection with FIG. 5, the solution emitting device 607 emits afountain 605 of metal plating solution that contacts a single side ofthe metallic foil strip 508 (i.e., first surface 503 a). After coming incontact with the metallic foil strip 508, the metal plating solutionspills off of the metallic foil strip 508 and is collected within theplating container 611. The solution emitting device is fluidly coupledwith the plating container 611 so that it can reuse the collected metalplating solution to continue to form the fountain 605.

Referring now to FIG. 6B, an exemplary way of forming and generating thefountain 605 is described. The described implementation helps limit themetal plating solution to a single side of the metallic foil strip 508by having some of the metal plating solution in the fountain 605 flowlaterally over the surface of the metallic foil strip 508. FIG. 6B is anenlarged view of the fountain 605 and a portion of the metallic foilstrip 508 of FIG. 5. In the illustrated embodiment, arrows 650 indicatethe direction of the flow of the metal plating solution that makes upthe fountain 605. As indicated by the arrow 650 a, the metal platingsolution is propelled towards the first surface 503 a of the metallicfoil strip 508. The metal plating solution is propelled with a moderateamount of force, such that gravity causes the stream of metal platingsolution to bend and spread out prior to reaching the metallic foilstrip 508. As indicated by the arrow 650 b, in portions of the fountain605 adjacent to the first surface 503 a of the metallic foil strip 508,the metal plating solution is flowing in a direction substantiallyparallel to the first surface 503 a. At the edges 653 of the region 652where the fountain 605 is in contact with the metallic foil strip 508,the angle of incidence between the incoming flow of metal platingsolution and the first surface 503 a is oblique (e.g., approximatelybetween 80° and 90°). This reduces the likelihood that metal platingsolution will curl around and come in contact with the second surface503 b of the metallic foil strip 508.

Although only a few embodiments of the invention have been described indetail, it should be appreciated that the invention may be implementedin many other forms without departing from the spirit or scope of theinvention. For example, FIGS. 2 and 4 describe plating systems that havemultiple components, such as tensioner and receiving drums, coils,cleaning stations, drying stations etc. Each of these components can beremoved, replaced, rearranged, multiplied and/or otherwise modified tosuit the needs of particular applications. For example, although thepath of the metallic foil strip in FIGS. 2 and 4 begins with a coil andends with a receiving drum, this need not be the case. In variousimplementations, the metallic foil strip may be fed into the system notin a coiled form, but in some other compact form, or fed uncoiled intothe system from another processing operation. In another implementation,the metallic metal strip, after being plated and dried, may not berecoiled, as depicted in the illustrated embodiments, but may be insteadarranged in a different compact form and/or a form that is appropriatefor further processing.

It should also be appreciated that any feature of a component in oneembodiment can be applied to a corresponding component in anotherembodiment. For example, although use of an elastic material for thesurface of the plating solution drum 110 was primarily described inconnection with FIG. 1, it should be appreciated that such a feature maybe used in connection with any of the described plating solution drums.The elastic surface may be formed from any elastic material that issuitable for use in an electroplating solution, such as silicone orrubber. Therefore, the present embodiments should be considered asillustrative and not restrictive and the invention is not limited to thedetails given herein, but may be modified within the scope andequivalents of the appended claims.

1. An apparatus for plating metal on a surface of a metallic foil foruse in semiconductor packaging, comprising: a container containing ametal plating solution; a plating solution drum positioned over thecontainer; a metallic foil strip having a first surface and an opposingsecond surface, portions of the metallic foil strip wound tightly andcompletely around the plating solution drum to form a metallic foil coilsuch that the first surface of the metallic foil strip is at leastpartially exposed to and immersed in the metal plating solution and thesecond surface of the metallic foil strip is pressed tightly against aturn in the metallic foil coil and does not come in substantial contactwith the metal plating solution; a first electrode electrically coupledwith the metal plating solution; and a second electrode electricallycoupled with the metallic foil strip, the first and second electrodesarranged to conduct an electrical current through the metal platingsolution and the metallic foil strip, wherein the apparatus is arrangedto rotate the metallic foil strip at least partially around the platingsolution drum and through the metal plating solution, the apparatusfurther arranged to plate metal from the metal plating solution onadditional portions of the first surface of the metallic foil stripduring said rotating without substantially plating metal on the secondsurface of the metallic foil strip.
 2. The apparatus of claim 1 whereina waterline of the metal plating solution is positioned below one ormore break points on the metallic foil strip where the metallic foilstrip starts to unwind from the plating solution drum and the secondsurface of the metallic foil strip starts to become exposed.
 3. Theapparatus of claim 1, wherein the plating solution drum is partiallysubmerged in the metal plating solution to a depth that is less than theradius of a cross section of the plating solution drum, thereby helpingto prevent the metal plating solution from slipping underneath a portionof the metallic foil strip that is unwinding from the plating solutiondrum.
 4. The apparatus of claim 1, wherein the plating solution drumincludes an elastic silicone surface, the silicone surface pressingagainst a portion of the metallic foil strip to help prevent metalplating solution from coming in substantial contact with the secondsurface of the metallic foil strip.
 5. The apparatus of claim 1 furthercomprising a tensioner drum, the metallic foil strip winding at leastpartially around the tensioner drum, the tensioner drum helping toincrease tension in the metallic foil strip, thereby helping preventmetal plating solution from reaching the second surface of the metallicfoil strip.
 6. The apparatus of claim 1 further comprising a receivingdrum positioned to receive portions of the metallic foil strip that havebeen in contact with the metal plating solution, the receiving drumarranged to wind portions of the metallic foil strip around thereceiving drum.
 7. The apparatus of claim 1 further comprising: a firstset of one or more cleaning stations, the first set of cleaning stationspositioned along a path of the metallic foil strip between the platingsolution drum and a receiving drum, the first set of cleaning stationsarranged to clean a section of the metallic foil strip after the sectionhas been plated; and a drying station positioned along the path of themetallic foil strip between one of the cleaning stations and thereceiving drum, the drying station arranged to dry portions of themetallic foil strip prior to the winding of the dried portions aroundthe receiving drum.
 8. The apparatus of claim 1 wherein the secondelectrode is a metallic brush arranged to maintain an electricalconnection with the metallic foil strip when the metallic foil strip isin motion.
 9. The apparatus of claim 1 wherein the metallic foil stripis made of copper and the metal plating solution is a silver platingsolution.
 10. The apparatus of claim 1 wherein an electricallynon-conductive material is applied on edges of the metallic foil stripto help prevent metal from plating onto the edges.
 11. The apparatus ofclaim 1, the apparatus further comprising: a receiving drum, a portionof the metallic foil strip being wound at least partially around thereceiving drum, the receiving drum arranged to recoil portions of themetallic foil strip that were unwound from the metallic foil coil; atensioner drum, the metallic foil strip winding at least partiallyaround the tensioner drum, the tensioner drum positioned along a path ofthe metallic foil strip between the plating solution drum and thereceiving drum and arranged to help increase tension in the metallicfoil strip and help press the metallic foil strip more firmly againstthe metallic foil coil; a set of one or more cleaning stationspositioned along a path of the metallic foil strip between the secondand the receiving drum, the second arranged to clean the section afterthe section has been plated; and a drying station positioned along thepath of the metallic foil strip between the set of cleaning stations andthe receiving drum, the drying station arranged to dry the section ofthe metallic foil strip after the section has been plated and cleaned.